Naming, sentence comprehension, and speech fluency are frequently impaired in patients with stroke, probable dementia of the Alzheimer's type, and Parkinson's disease. The purpose of this project is to decompose complex language skills such as these into more fundamental, linguistically- motivated processes, and to begin to establish the cerebral basis for impairments in these processes using modern neurophysiologic techniques. Specifically, complex language skills such as naming will be fractionated into more basic linguistic processes, and the nature of these processes will be validated within and across groups of subjects using paper-and- pencil testing techniques. The cerebral localization of these processes will be determined by several measures of regional cerebral metabolism using positron emission tomography. The contribution of neurochemical indices to language functioning will be established by direct measurements of neurotransmitter levels in the cerebrospinal fluid. The results of the proposed studies are expected to show that complex language skills can be decomposed into more basic processes. Impairments of qualitatively similar processes will be observed across several patient groups. Each group of subjects is expected to manifest a unique clustering of these processing impairments. A deficit in performing a specific linguistic process is expected to be related to reduced metabolism in a particular cerebral region. Networks of brain regions will be seen to work together in order to support the performance of a complex skill like naming. Moreover, changes in neurotransmitter receptor densities and cerebrospinal fluid levels are expected to be correlated with specific language processing impairments. These studies will contribute to our understanding of the cerebral basis for our language capacity, and will provide a rational basis for the development of therapeutic strategies to help individuals with language impairments.